a) Field of the Invention
The invention relates to microscope tubes for switchable binocular observation and photographic recording or connection to video cameras. Such microscope tubes are often constructed with only two possible switching positions. This is because of the required tube width which is usually already equal to three prism widths when there are two switching positions and to approximately five prism widths when there are three switching positions. Assuming a prism width of 30 mm, this means that the width space requirement is 150 mm. However, many applications require 100-percent observation, 100-percent photography and a determined divider ratio between the two operating modes for simultaneous availability of both binocular beam paths being available simultaneously.
b) Description of the Related Art
In U.S. Pat. No. 2,910,913, a continuous beam path, a partially reflecting prism and a fully reflecting prism are arranged side by side in an arrangement that is very wide spatially. This arrangement is not very advantageous in terms of appearance, space requirement and material. In addition, a wider tube restricts accessibility and visibility of other controls on the microscope.
EP 85317 A1 describes a slide which can be switched to three positions and which moves a prism into the beam path; this also has a disadvantageous effect on the tube width.
DE 3636616 A1 provides two prisms and a switchable mirror which must be driven in a relatively complicated manner by separate drive units.
DE 3318011 C2 is directed to an auxiliary device for stereo microscopes with controls in a plurality of planes and different, complicated guide means.
Utility Model DE 8712342 U1 contains a prism slide which is only displaceable between two positions.
U.S. Pat. No. 4,685,776 provides three prisms adjacent to one another in the beam path for realizing the visual function, photo function, and joint visual/photo function. In this case also, there is a space requirement of five prism widths when switching, which restricts handling and takes away space that could be used for other additions.
Reference is had to the entire disclosure of DE 196 22 357, which provides a solution having two prisms which are individually displaceable relative to one another and, in addition, a compensating plate. While this solution requires only three prism widths for the three switching positions, its construction is mechanically complicated because of the two individually displaceable prisms and the compensating plate that is needed for adapting to the different glass paths. Further, switching generally requires that two actuating elements be moved; that is, both hands must be used.